Oxycombustion flue gases are generally purified using a separation step at subambient temperature to produce pure CO2. Upstream of the separation step the flue gas is purified by adsorption to remove water. The adsorption unit typically comprises two beds which operate according to a cycle, the cycles being timed so that the flue gas can be purified at all times. It is necessary to regenerate the adsorption unit by sending a dry gas through the bed to eliminate the accumulated humidity.
The dried flue gas is sent from the adsorption unit to the separation unit to be separated by subambient temperature distillation using at least one phase separator and/or a distillation column. Non condensable gases are removed from the separation unit and still contain a significant portion of CO2. CO2 can be recovered from these non-condensable gases via a permeation device, an adsorption device (Pressure Swing Adsorption or Vacuum Pressure Swing Adsorption). The dried flue gas typically contains at least 65% carbon dioxide or even at least 70% carbon dioxide and at least 1% oxygen. A maximum percentage for the carbon dioxide content could be 95%.
It is known from U.S. Pat. No. 8,012,446 to regenerate the adsorption unit with the permeate of a membrane device at low pressure and recycle the permeate to the boiler or the environmental island. This allows for impurities regenerated from the dryer to be efficiently handled in the environmental island or the boiler itself (desulfurization steps and/or combustion in the boiler and/or NOx production mitigation in the boiler).
It is also known from WO-A-2007/126972 to separate the feed in a phase separator and send the liquid formed to a distillation column producing pure carbon dioxide. In this case, the gas from the phase separator is mixed with the column top gas and used to regenerate the adsorption unit.
EP-A-0596470 describes a process according to the preamble of Claim 1.